Olt, the No. 2 ranked prospect in the farm system by MLB.com, is undergoing tests on his eyes after he reported some vision problems over the weekend. He has not been in the Round Rock lineup since Thursday. Olt is currently hitting .139 with one home run and six RBIs in 20 games. He has struck out 32 times in 72 at-bats and the Rangers can't help wonder if his vision has been a factor.

"It would make more sense," general manager Jon Daniels said. "But we'll wait until we get an official diagnosis and hold off any conclusions."

Buckel, who is the club's No.4 prospect, is healthy but pitching poorly at Frisco. So the Rangers are going to put him in the bullpen to see if he can work out his problems. He has walked 25 batters in nine innings over five starts.

"He's been putting the bullpen in a tough spot, making them pick up a lot of innings," Daniels said. "It's the nature of the game. Guys have ups and downs. There aren't too many guys who get there without any hiccups."